Power control based admission methods for maximum throughput in DS-CDMA networks with multi-media traffic

ABSTRACT

A method for maximizing the data throughput over a multi-code DS-CDMA network by controlling the number of codes assigned to each user while controlling the power budget of each user so that each users bit energy to noise ratio is met along with the quality of service and frame error rate requirements. A method is also provided for maximizing the throughput over a variable gain DS-CDMA network in which each user uses only one code and changes the data rate and power to meet quality of service requirements. In both systems, new users will be admitted so long as the power budget and bit energy to noise ratio requirements of each user is maintained. Both systems become closed to new admissions if the addition of a new user would cause any active user to not meet its required performance.

[0001] The present application claims priority based on the provisionalapplication Ser. No. 60/169,849, filed on Dec. 9, 1999, the entirecontents of which are incorporated herein by reference. The presentinvention relates to a method for jointly controlling the data rates andtransmit power of users so as to maximize throughput in cellular DirectSequence Code Division Multiple Access (DS-CDMA) networks. The inventionis applied to both multi-code (MC-CDMA) and variable gain (VG-CDMA)systems in order to maximize throughput in both systems.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION

[0002] There is an increasing use of multi-media transmissions overcellular CDMA networks. However, a CDMA cellular network is by its verynature interferences limited. The layering of each signal across theavailable bandwidth increases the interference and affects the overallbandwidth utilization.

[0003] Attempts have been made in the past to limit the amount ofinterference by limiting the number of network users. This obviouslyaffected the throughput of the network and also adversely affected newadmissions to the network.

[0004] In a CDMA environment, in order to provide efficient bandwidthutilization the resources of the users that can be controlled aretransmit power and data rates. The approach of power based admissionpolicies has been to determine if a new potential user and existingusers have sufficient power budgets to allow the new potential user totransmit at the requested data rate. Each user has an information bitenergy to noise ratio that must be met in order to achieve desiredquality of service requirements. It has been found, however, that theusers cannot typically be allowed to transmit at their full transmitpower capability since this adds unnecessary interference to the system,which in turn limits the number of possible users and the datathroughput. Thus, the transmit power of each user has to be controlledto limit interference while at the same time allowing sufficient powerto meet the users requirements

[0005] Besides power, the second user resource that can be controlled tomaximize usage of the CDMA network is the data rate of the user. Twosystems have been proposed for controlling the data rate. In amulti-code Code Division Multiple Access (MC-CDMA) system, each useroperates at a fixed data rate using one or more codes to carry theinformation. The processing gain of each user is the same since the datarate is fixed. Processing gain is defined as the ratio between thesignal baseband bandwidth and the spread spectrum bandwidth. Usersattain higher data rates by using multiple codes simultaneously. In aVariable Gain Code Division Multiple Access ( VG-CDMA) system, only onecode is used by each user and the data rate is changed to meet the usersdata transfer requirements. The processing gain of the system changesinversely with the data rates. In both variable gain and multicode CDMAnetworks, provisions must be made to control the admission of new usersin order for the system to operate at maximum throughput. The quality ofservices and Frame Error Rate of the user is dependent on the receivedbit energy to noise power ratio. Therefore, the admission strategy mustensure that the received bit energy to noise ratio for all user codesthat are activated is above the required threshold.

[0006] A detailed mathematical analysis of the derivation of thealgorithms for controlling the data rates and transmit power of users,so as to maximize throughput in cellular DS-CDMA networks is presentedin the following references, which are hereby incorporated herein byreference in their entirety.

[0007] 1) D. V. Ayyagari and A. Ephremides in Power Control BasedAdmissions Algorithms for Maximizing Throughput in DS-CDMA Networks withMulti-Media Traffic. IEEE-WCNC 1999, Sep. 25, 1999.

[0008] 2) D. V. Ayyagari, Capacity and Admission Control in Multi-MediaDS-CDMA Wireless Networks. Ph.D. Dissertation, University of Maryland,College Park, 1998.

SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, an optimum system andmethod are provided for the admission of new users to a datalink usingmulti-code Code Division Multiple Access (MC-CDMA) and variable gainCode Division Multiple Access (VG-CDMA) networks. The MC-CDMA admissionprocess is much simpler since all users of the network are using thesame data rate and have the same processing gain. The VG-CDMA admissionprocedure is complicated by the use of varying data rates, depending onthe type of information being transmitted over a multi-media data link,which cause the processing gain to vary inversely to the data rate.However, the variable gain procedure can be substantially simplified ifa less than optimum solution is acceptable. A less than optimumtechnique is also taught herein. Both systems tend to maximizethroughput through their respective CDMA networks.

[0010] Most generally, the inventive system comprises a plurality ofusers having different bit energy to noise requirements. There is alimited capacity, defined in terms of number of codes or data rates onindividual codes available to be used by the network for allocation tousers, the limit being determined by the constraint of meeting the bitenergy to noise requirements of the active users. There is also alimited overall power allocation available for each of the potentialcodes. An admission protocol maximizes capacity utilization within thenetwork with the limited overall power budget.

[0011] With respect to an MC-CDMA network the admission protocolarranges the networks in increasing order based on the bit energy tonoise requirements. It includes the testing of multiple potential codesfor generally simultaneous activation, the number of multiple potentialcodes being reduced until an acceptable threshold is met, the thresholdbeing limited by the overall available power allocation such thatnetwork failure is minimal for the existing active codes within thenetwork.

[0012] For a VG-CDMA network the users are further broken down intousers at different powers, the users being separated into differentpower groups as well as users at different data rates, the users beingseparated into different data rate sets. In a preferred teaching, theallocation protocol includes users in two different power groups andthree different rate groups, two of the rate groups calculated in termsof the third rate group.

[0013] The network of the invention is discussed most specifically withrespect to cellular applications. However, the various methodologies areequally applicable to local area networks, wide area networks,metropolitan area networks and fixed wireless networks.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a flowchart showing the steps to optimizing throughputthrough a multi-code DS-CDMA network.

[0015]FIG. 2 is a flowchart showing the steps in optimizing data rateand power in a variable gain DS-CDMA network.

DETAILED DESCRIPTION

[0016] Efficient bandwidth utilization is necessary to providemulti-media services on a cellular CDMA platform. In a CDMA environment,the resources of the users that can be controlled to provide the mostefficient bandwidth utilization are the transmit powers and the datarates.

[0017] The most important attribute of the multi-code MC-CDMA system isthat the data rate and hence the processing gain of each code is thesame. Users attain higher data rates by using multiple codessimultaneously. The Frame Error Rate of the users is dependent on thereceived bit energy to noise power ratio E_(b)/N₀. Frame Error Rate is ameasure of errors made in transmitting between a mobile unit and a basestation while the received bit energy to noise power ratio is the signalto noise ratio necessary for two way communication. Therefore, anadmission policy must ensure that the received E_(b)/N₀ for all usercodes that are activated, is above a required threshold. In thefollowing, “activation” of a code means the particular mobile user isassigned a power level and given permission to transmit at a fixed datarate by a cellular network base station (“BS”). Activation of the newcode also implies that all the codes that are currently active cancontinue to remain active.

[0018] Each mobile user has constraints on the minimum and maximumnumber of codes that can be used as well as a limitation on the maximumtransmit power. The maximum received power is a function of the handsettransmitter peak output power and the propagation gain from the user'scurrent location (collectively, transmit power plus path gain and thesystem losses, is the user's power budget). A code allocation oractivation is said to have a feasible or acceptable power allocation ifthe power that would be required by all active users upon activation ofthe new code, is equal to or less than the maximum transmission powercapability of the users and the E_(b)/N₀ minimum threshold target is metfor all active codes. Ideally, a power is selected that works the bestwhile producing the least amount of interference.

[0019] The objective of an admission policy based on rate allocation isto determine the code allocation such that the overall traffic carriedby the system is maximized, that is, the sum of the data rates allocatedto all the users is maximized. Since the data rate per code is fixed,the reward function that must be optimized by the admission policyequals the sum of the number of codes activated for all users.

[0020] Since each code has the same data rate R in a MC-CDMA network,the reward function appreciates by R, irrespective of the user who wasallocated the new code. However, the effect of admitting the new code onthe active user powers depends on the E_(b)/N₀ target of the admitteduser. Peak capacity is reached when one or more users become powerlimited. Therefore, the admission policy must activate the code with theleast impact, in terms of increases in power levels and interferences,in order to improve the capacity. Ideally, a user is added thatcontributes the least amount of interference. The policy modulates thesignal and spreads it across the entire bandwidth. The signals arelayered on top of one another.

[0021] The method of the present invention is shown, in a MC-CDMAenvironment in FIG. 1, where 5 shows a queue of mobile users (“MS”) thathave requested the base station for permission to transmit data packets.These MS have also specified to the BS their maximum and minimum datarate requirements (by other means such as out-of-band signaling orcontention access on control channels) admission to the network from thebase station

[0022] The base station begins the admission process at 7 where itassigns the minimum feasible number of requested codes to the mobileuser with the lowest signal to noise ratio requirement.

[0023] A code activation is said to have a feasible power allocation ifthe power requested for the activated code is less than the maximumpower for all codes and the signal to noise ratio targets are met forall active codes.

[0024] The base station continues admitting users from the queue inprogressively increasing order of signal to noise ratios in order tomaximize the number of new codes that can be activated. At point 9, thebase station computes the minimum power levels of the new codes to beactivated and the new powers of all active users, which change tocompensate for the interference caused by the addition of new users tothe network. Thus, the network computes the minimum transmit powerrequired by all active codes and all proposed additional codes caused bythe addition of new users to the network.

[0025] The minimum transmit power required can be computed easily fromthe minimum received power required to maintain a desired E_(b)/N₀ foreach active user and from their link budgets.

[0026] Without loss of generality, let there be M users with activecodes or codes being considered for activation and let s₁ be thereceived power from the i-th user. If W is the spread spectrum bandwidthand R is the data rate per code and c₁ is the number of codes active orbeing activated for the i-th user, the minimum received powers requiredby all M users s₁-s_(M) are given by:$\frac{\frac{W}{R} \times s_{i}}{{\sum\limits_{j \neq i}{c_{j}s_{j}}} + {\left( {c_{i} - 1} \right)s_{1}} + \eta} = \gamma$

[0027] where the E_(b)/N₀ of the i-th user is γ₁ and η is the sum of outof cell interference power and thermal noise. The notation “j”represents all users who are different form the “ith” user beingconsidered in the equation. The summation in the denominator representspowers from all other users excluding user “i”. The minimum transmitpower required is then obtained as follows:

Transmission Power (Tx)=Received Power (Rx)+Path loss+System losses

[0028] The base station also makes sure that no mobile station that iscurrently active is power limited. If any of the active mobile usersrequire power greater than the maximum transmit power of any mobile userat point 11, the base station refuses admission at point 13.

[0029] If the minimum power required is not greater than the maximumpower for any active mobile user MS, at point 15 the base stationactivates the codes requested for a proposed user. At 17, the basestation continues the code activation process for additional codes ofthe same user in steps of 1, testing at point 19 that the number ofcodes activated do not exceed the maximum number requested by the mobilestation. Thus, the base station looks at the addition of codes one at atime up to the maximum number of codes desired by a user.

[0030] On the acceptance of each set of new codes, as shown by arrow 21,the base station determines that the power to be allocated to thedesired codes is within the maximum power capability of all the activemobile stations at point 11 as discussed above and either activates thecodes at point 15 or rejects the proposed codes at point 13. When themaximum number of codes has been activated, the base station terminatesthe admission process for that particular user and returns to point 5 toconsider a new user. The new user is the user in the request queue withthe lowest signal-to-noise (“SNR”) requirement. In case of a tie, theuser may be chosen arbitrarily or based on the lowest number of codesrequired. As the process continues, the base station also continuouslymonitors the state of the network. In particular, as codes are activatedor become deactivated, it adjusts the power level for all active usersto ensure that they stay above their signal to noise ratio limit.

[0031] As the base station determines that the admission process isapproaching the end for a particular user, it can test to see if afeasible power allocation exists by the simultaneous activation of aminimum number of codes. The base station tests that the powerallocation requested is less than the maximum power allocated to theuser. If not, the base station rejects the codes being considered foractivation and terminates the admission process.

[0032] By testing the feasibility of each set of codes considered foractivation, the base station ensures that each user is operating at theoptimal power level and that the network is operating at its maximumthroughout having the maximum number of activated codes.

[0033] Most generally, the DS-CDMA network comprises a plurality ofusers having different bit energy to noise requirements. There is alimited capacity, defined in terms of number of codes or data rates onindividual codes available to be used by the network for allocation tousers, the limit being determined by the constraint of meeting the bitenergy to noise requirements of the active users. There is also alimited overall power allocation available for each of the potentialcodes. An admission protocol is used to maximize the capacityutilization within the network with the limited overall power budget. Incontrast to a MC-CDMA network where the activation of each new code aspart of the admission protocol adds a discrete block of data rate to thereward function, in a VG-CDMA network the data rate added as part of anadmission protocol depends on the type of information that eachmulti-media user wishes to transmit. In a VG-CDMA network each user isassigned a single code. The data rate of the single code depends on themode of information being transmitted. For example, the transmission ofvideo information would use a much higher data rate than thetransmission of voice information. In a VG-CDMA network both the datarate per code and power level are changed. The reward function that ismaximized is the sum of the data rates of all active users.

[0034] Each user's data rate requirements are based on the type ofinformation to be transmitted (e.g. voice, data, or video). The basestation activates a code or specifies a particular data transmissionrate for the code for each user with the goal of maximizing throughputwithin the power constraints of the system. Higher data rates requirehigher power. Therefore, the base station must control both the datarate, by user selection, and the power of the users to maximizethroughput.

[0035] The following is a brief outline of the steps, illustrated inFIG. 2, used to calculate the optimum data rate and power before thepresentation of the detailed mathematical procedures.

[0036] The process begins in step 23, where all the requests forbandwidth from the different mobile users are queued at the basestation. The requests specify the maximum and minimum power capabilitiesof the mobile users as well as the minimum and maximum data raterequirements.

[0037] Next, at step 25, data rates to be assigned to the users are allderived or expressed in terms of the received powers the base stationrequires from all of the mobile users. As a result, it is only necessaryto determine the powers to be assigned to be able to determine both datarates and powers for each user.

[0038] In step 27 the users are arbitrarily classified into power groupsIn the preferred embodiment, the two power groups used are either (i)maximum power limited or (ii) not maximum power limited. As discussed ingreater detail below, well-reasoned heuristic choices can simplify thedecision-making process. A maximum power limited user is a user who isrequired to transmit at his maximum power while a user who is not powerlimited will be told by the base station to transmit at a power lessthan his maximum.

[0039] After step 27, the mobile users are then classified in step 29into three groups based on the data rates that the base station willassign them. The first set, P1, consists of users assigned data rateswhich are in between minimum and maximum rate requirements of the users.P2 consists of users assigned a minimum data rate and P3 consists ofusers assigned a maximum data rate.

[0040] Next, as illustrated in step 31, using constants, the powers ofall users in P2 and P3 can be expressed in terms of powers of users inP1. Then in step 31 powers of all users in P1 are expressed in terms ofthe power of a single user in P1 and the total in-cell interference β.

[0041] Once the powers of all users in P1 has been restated, then instep 35, the power of the single user, which remains undetermined instep 31, is computed for a certain in-cell interference β, which is thetotal interference generated from within the cell (sum of powers of allactive mobile users in cell) that can be tolerated by the network.

[0042] In Step 37, the system begins to work its way back to determinethe powers and data rates of the remaining users. As shown in step 37,the system derives the powers for all users in sets P1, P2 and P3 usingthe relations established in steps 31 and 33. Then in step 39, the datarates are derived using the relations established in step 25. Atdecision point 41, the system loops back to step 27 and performs steps29 through 39 for a new classification of users in terms of powers anddata rates. This loop is performed until all possible classifications ofusers into the different power and data rate sets are exhausted.

[0043] Finally, at step 43, the system determines the power and datarate allocation for the classification that yields the highest sum ofdata rates of all users. This is the final data rate and powerassignment made by the base station to the mobile users requestingbandwidth.

[0044] The above procedure is computationally intense as the number ofcombinations of the discussed classifications of power groups and rategroups grows exponentially with the number of users M.

[0045] The following is a mathematical analysis of the steps leading upto the optimal rate and power solution. Let M denote the number of usersrequesting bandwidth. The spread spectrum bandwidth is W. Each user usesa single code. Let r_(i) denote the data rate assigned to the user i.The processing gain of the code used by the user i is $\frac{w}{r_{i}}.$

[0046] Based on the date rate requirements of the applications, the datarates are constrained by minimum and maximum rate requirements. Letr_(i) ^(min) and r_(i) ^(max) denote the minimum data rate and maximumrate respectively, required by the user i. Within the VG-CDMA networkr_(i), is a continuum while in the MC-CDMA network the number of codesc_(i) is discrete. The rate allocation vector for the M users is denotedby r. Let γ_(i) denote the Eb/N0 threshold for user i. Also defineT_(i)=γ_(i)*r_(i)/W.

[0047] The received power per code from the ith user is s_(i). Lets^(max)=└s₁ ^(max)s₂ ^(max). . . S_(M) ^(max)┘ be the peak receivedpower vector. s_(i) ^(max) is a function of the handset transmitter peakoutput power and the propagation gain from the user's current location(the user's power budget). Note that S_(i) ^(max) can change with thelocation and velocity of the user, as the channel conditions between theuser and the base station vary. Let η represent the thermal noise plusout-of cell interference power. Let s denote the vector of receivedpowers for the M users. The power allocation associated with a data rateallocation r is referred to as s(r). A data rate allocation r is said tobe “feasible,” if there exists a power vector s(r)≦s^(max).$\left( \frac{E_{b}}{N_{o}} \right)_{i} = {\frac{\frac{w}{r_{1}} \times s_{i}}{{\sum\limits_{j \neq 1}s_{j}} + \eta} \geq \gamma_{i}}$

[0048] The objective of the admission control policy is to determine therate vector r such that the overall traffic carried by the system ismaximized i.e., the sum of the data rates allocated to the M users (or asubset of the M users) is maximized. When a user's data rate isincreased by the admission policy, the processing gain decreases and thequantity T_(i) increases. In the MC-CDMA network T_(i) remainsunaffected as codes are assigned to the user i. As the T_(i) valueincreases, the users require higher powers to maintain Quality ofService (QoS) as compared to power levels required to sustain the sameincrease in data rate for a user having a lower T_(i). $\begin{matrix}{r_{i}^{*} = \frac{\frac{w}{s_{i}^{*}} \times \gamma_{i}}{{\sum\limits_{j = {{1j} \neq 1}}^{M}s_{j}^{*}} + \eta}} & (1)\end{matrix}$

[0049] The optimal rate vector r* can be determined if the powerallocation s* is determined. The users are classified in groups based ontheir rate and power allocations as below Define the following sets:

Φ={users i: s _(i) ^(*<) s _(i) ^(max)}  (2)

Π₁={users i:r _(i) ^(*) ≠r _(i) ^(max) ,r _(i) ^(*) ≠r _(i) ^(min)}  (3)

Π₂={user i:r _(i) ^(*) =r _(i) ^(min)}  (4)

Π₃={user i:r _(i) ^(*) =r _(i) ^(max)}  (5)

[0050] The set Φ represents those mobiles that are operating at theirmaximum received power at the optimal rate-power allocation. Similarly,the sets Π classify the users based on their data rates at the optimalallocation. The complement of set X is denoted by X′.

[0051] The powers of the users belonging to sets Π₂ and Π₃ can beexpressed in terms of the powers of users in set Π₁ by using equation(1). $\begin{matrix}{{Ws}_{j}^{*} - {r_{j}^{\min}{\gamma_{j}\left( {{\sum\limits_{{i \in \Pi_{2}},{i \neq j}}s_{i}^{*}} + {\sum\limits_{i \in \Pi_{1}}s_{i}^{*}}} \right)}} + {r_{j}^{\min}{\gamma_{j}\left( {{\sum\limits_{i \in \Pi_{1}}s_{i}^{*}} + \eta} \right)}{\forall\quad {j \in \Pi_{2}}}}} & (6) \\{{Ws}_{j}^{*} - {r_{j}^{\max}{\gamma_{j}\left( {{\sum\limits_{{i \in \Pi_{3}},{i \neq j}}s_{i}^{*}} + {\sum\limits_{i \in \Pi_{2}}s_{i}^{*}}} \right)}} + {r_{j}^{\min}{\gamma_{j}\left( {{\sum\limits_{i \in \Pi_{1}}s_{i}^{*}} + \eta} \right)}{\forall\quad {j \in \Pi_{3}}}}} & (7)\end{matrix}$

[0052] These are a set of N linear equations (N=|Π₂|+|Π₃|), in Nunknowns (powers of the users in sets Π₂ and Π₃). Therefore, solving forthe powers of the users in set Π_(i) will result in determining theoptimal rate and power allocation. The powers of the users in set Π₂ maybe expressed as follows: $\begin{matrix}{s_{i} = {{f_{j}\left( {{\sum\limits_{i \in \Pi_{i}}s_{i}^{*}} + \eta} \right)}{\forall\quad {j \in \Pi_{2}}}}} & (8) \\{f_{j} = {{r_{j}^{\min}{\gamma_{j}\left( {\frac{1}{W + {r_{j}^{\min}\gamma_{j}}} + \frac{r_{j}^{\min}\gamma_{j}}{{x\left( {W + {r_{j}^{\min}\gamma_{j}}} \right)}^{2}}} \right)}} + {\left( \frac{r_{j}^{\min}\gamma_{j}}{{x\left( {W + {r_{j}^{\min}\gamma_{j}}} \right)}^{2}} \right)\quad \left( {{\sum\limits_{j \in \Pi_{2}}{r_{j}^{\min}\gamma_{j}}} + {\sum\limits_{j \in \Pi_{3}}{r_{j}^{\max}\gamma_{j}}}} \right)}}} & (9) \\{x = {1 - {\sum\limits_{j \in \Pi_{2}}{r_{j}^{\min}{\gamma_{j}\left( {W + {r_{j}^{\min}\gamma_{j}}} \right)}}} + {\sum\limits_{j \in \Pi_{3}}{r_{j}^{\max}{\gamma_{j}\left( {W + r_{j}^{\max}} \right)}}}}} & (10)\end{matrix}$

[0053] The terms ƒ_(i) are independent of all power terms. The powers ofthe users in set Π₃ may be expressed as follows: $\begin{matrix}{s_{j} = {{f_{1}\left( {{\sum\limits_{i \in \Pi_{1}}s_{i}^{*}} + \eta} \right)}\quad {\forall\quad {j \in \Pi_{3}}}}} & (11) \\{f_{j} = {{r_{j}^{\max}{\gamma_{j}\left( {\frac{1}{W + {r_{j}^{\max}\gamma_{j}}} + \frac{r_{j}^{\max}\gamma_{j}}{{x\left( {W + {r_{j}^{\max}\gamma_{j}}} \right)}^{2}}} \right)}} + {\left( \frac{r_{j}^{\max}\gamma_{j}}{{x\left( {W + {r_{j}^{\max}\gamma_{j}}} \right)}^{2}} \right)\quad \left( {{\sum\limits_{j \in \Pi_{2}}{r_{j}^{\min}\gamma_{j}}} + {\sum\limits_{j \in \Pi_{3}}{r_{j}^{\max}\gamma_{j}}}} \right)}}} & (12) \\{x = {1 - {\sum\limits_{j \in \Pi_{2}}{r_{j}^{\min}{\gamma_{j}\left( {W + {r_{j}^{\min}\gamma_{j}}} \right)}}}\quad + {\sum\limits_{j \in \Pi_{3}}{r_{j}^{\max}{\gamma_{j}\left( {W + r_{j}^{\max}} \right)}}}}} & (13)\end{matrix}$

[0054] Since the powers of the users belonging to set Φ′ are known to bes_(i) ^(max), we need to determine the powers of the users i that arebelong to both sets Φ and Π_(i). The following result helps determinethe required powers for user i.

[0055] Let us define the following: $\begin{matrix}{I_{1} = {{\sum\limits_{j \neq 1}s_{i}^{*}} + \eta}} & (14)\end{matrix}$

[0056] I_(i) is the effective interference experienced by the user i.Also, let $B = {\overset{M}{\sum\limits_{i = 1}}{s_{i}^{*}.}}$

[0057] B is a measure of the total interference generated by users inthe sector. From the definition of I_(i), we know that I_(i)=B+η+s_(i).Therefore, the powers of all users k, k ≠ i, can be expressed in termsof a single user i. $\begin{matrix}{s_{k} = {{\left( {B + \eta} \right)\quad \left( {1 - \sqrt{\frac{\gamma_{1}}{\gamma_{k}}}} \right)} + {s_{i}\sqrt{\frac{\gamma_{i}}{\gamma_{k}}}}}} & (15)\end{matrix}$

[0058] The powers for the users j in sets Π₂ and Π₃ can be expressed interms of the power s_(i) of user i in by using (15), (8) and (11).$\begin{matrix}{s_{j} = {f_{j} \times \left( {{s_{i}\left( {\sum\limits_{k \in \Pi_{1}}\sqrt{\frac{\gamma_{i}}{\gamma_{k}}}} \right)} + {\sum\limits_{k \in \Pi_{1}}{\left( {B + \eta} \right)\left( {1 - \sqrt{\frac{\gamma_{i}}{\gamma_{k}}}} \right)}}} \right)}} & (16)\end{matrix}$

[0059] Now we need to determine the power s_(i) of user i. The powers ofall the other users can be determined from (15) and (16). Since${B = {\sum\limits_{u = 1}^{M}s_{i}}},$

[0060] we have the following: $\begin{matrix}{{B - {\left( {{\sum\limits_{k \in {({\Phi\bigcap\Pi_{1}})}}{\left( {B + \eta} \right)\left( {1 - \sqrt{\frac{\gamma_{1}}{\gamma_{k}}}} \right)}} + {\sum\limits_{j \in {({\Phi\bigcap\Pi_{1}})}}s_{j}^{\max}}} \right) \times \left( {1 + {\sum\limits_{j \in \Pi_{2}}f_{j}} + {\sum\limits_{j \in \Pi_{3}}f_{j}}} \right)} - {\eta \left( {{\sum\limits_{j \in \Pi_{2}}f_{j}} + {\sum\limits_{j \in \Pi_{3}}f_{j}}} \right)}} = {{s_{1}\left( {\sum\limits_{k \in {({\Phi\bigcap\Pi_{1}})}}\sqrt{\frac{\gamma_{1}}{\gamma_{k}}}} \right)}\left( {1 + {\sum\limits_{j \in \Pi_{2}}f_{j}} + {\sum\limits_{j \in \Pi_{3}}f_{j}}} \right)}} & (17)\end{matrix}$

[0061] The mathematical results that are derived above may be used todetermine the optimal power-rate allocation as follows:

[0062] Consider all possible combinations of users resulting in the setsβ, Π₁, Π₂ and Π₃. For each such combination of these sets as defined inequations (3-5) compute as follows:

[0063] Using equations (9-12) determine the constant coefficients ƒ_(i),which relate the powers of the users in sets Π₂ and Π₃, to the powers ofusers in set Π₁.

[0064] Using equation (17) determine the power s_(i).

[0065] Using equation (15) determine the powers of the other users in Π₁and then, using equation (16) determine the powers of the users in Π₂and Π₃.The only remaining variable is the total interference power B.Powers of all users in the sector are functions of B alone.

[0066] Determine the optimal power vector using the maximum value of B.This would depend on the peak-received powers from all mobiles or theinterference threshold established in order to limit interference toneighboring sectors.

[0067] Using equation (1) determine the optimal rate allocation for theparticular choice of sets.

[0068] Compare the rate allocations so determined for all possiblecombinations of the above sets to determine the optimal rate allocation.

[0069] The above procedure is computationally intense as the number ofcombinations of the set Φ, Π₁, Π₂ and Π₃ that result grows exponentiallywith the number of users M.

[0070] When the data rate constraints of the users are removed, theoptimization approach discussed above is considerably simplified as thesets Π₂ and Π₃ are empty. Since the complexity of the optimal solutionlies in having to consider all possible combinations of the sets Φ, Π₁,Π₂ and Π₃, approximate solutions may be obtained by intelligentheuristic choices of these sets.

[0071] The set Φ′ comprises of all users who operate at the maximumpower. The candidate user for the set Φ′ may be chosen from users whohave low power budgets and are likely to operate at maximum power. Inpractice, location plays a significant factor in this determination. Auser at a remote location relative to the nearest reception/transmissioncell of the network is most likely required to operate at maximum poweras opposed to users closely adjacent such a cell. Users having highvalues of y, are more likely to belong to set Φ. Also, consider theratios$T_{i}^{\max} = {{\frac{\gamma_{i}}{W/r_{i}^{\max}}\quad {and}\quad T_{t}^{\max}} = {\frac{\gamma_{i}}{W/r_{i}^{\min}}.}}$

[0072] When users with higher T_(i) ^(min) are serviced, this results ina higher increase in powers and interference as compared to servicingusers with lower T_(i) ^(min). Therefore, the users with lower T_(i)^(m)n may be chosen as candidates for the set Π₃. Users with lowervalues of T_(i) ^(max) are more likely in set Π₂. Users between thevalues of T_(i) ^(min) and T_(i) ^(max) are assigned to set Π_(i). Oncethe sets Φ, Π₁, Π₂ and Π₃ are determined, based on these heuristicarguments, the steps in the optimal approach can be followed todetermine the rate and power allocations.

[0073] The teachings presented herein provide efficient methods ofassigning users data rates while improving the capacity of a DS-CDMAsystem. The optimal allocation algorithm in MC-CDMA networks can beeasily implemented. For VG-CDMA networks, the problem is considerablysimplified by the absence of rate constraints. Even with theconstraints, a methodology has been proposed that, while computationallyintense, is guaranteed to yield the optimal rate-power allocation. Animportant result is that for the optimal allocation, the ratio ofinterference experienced by two users is equal to the square root of thereciprocal of their γ targets. This result may be used in heuristicbased algorithms to yield power allocations, which are sub-optimal butstill provide high capacity. Sub-optimal algorithms for VG-CDMA networksare easy to implement and may be expected to provide significantimprovement in capacity.

[0074] The above systems have been described for a cellular environment.But they are just as applicable, for example, in a fixed wirelessenvironments using CDMA, including and not limited to locally areanetworks, wide area networks and metropolitan area wireless networks.When in a fixed wireless environment, it is possible to replace thenumber of mobile users with the number of fixed wireless terminals andthen perform the teachings of the disclosed invention for efficientpower and admission control in the fixed wireless network using CDMA.

[0075] While the invention has been disclosed in connection with thepreferred embodiments shown and described in detail, variousmodifications and improvements thereon will become readily apparent tothose skilled in the art. Accordingly, the spirit and scope of thepresent invention is to be limited only by the following claims.

What is claimed is:
 1. An admission control procedure for traffic in aDS-CDMA system comprising the following steps: a) admitting to thesystem and activating codes for users with increasing order of signal tonoise ratios starting with the lowest signal to noise ratio; b)determining the power level of all active users and raising the powerlevels to compensate for the interference caused by the admission of newusers; and c) activating new codes in steps of one while ensuring noactive user is power limited.
 2. An admission control procedure as setforth in claim 1 wherein the admission control procedure activates thecode with the least impact on power levels and interferences.
 3. Anadmission control procedure as set forth in claim 1 wherein theadmission control procedure is terminated when at least one user becomespower limited.
 4. An admission control procedure as set forth in claim 1wherein the power levels of active users is reduced as codes leave thesystem.
 5. An admission control procedure as set forth in claim 1wherein the DS-CDMA system is one of local area network, wide areanetwork, metropolitan area network and a fixed wireless network.
 6. Aprocedure for admission control in a DS-CDMA network comprising thefollowing steps: a) arranging network users in increasing order based ontheir bit energy to noise requirements; b) beginning network admissionwith a first network user and allocating as many codes as requested andfeasible; c) continuing network admission for each consecutive networkuser; and d) testing to see if an additional number of potential codescan be activated simultaneously and if an acceptable overall powerallocation exists for each of the potential codes, comprising thesub-step of activating the potential codes if the acceptable overallpower allocation exists and the sub-steps of rejecting the potentialcodes and terminating network admission if the acceptable overall powerallocation does not exist.
 7. A procedure for admission control as setforth in claim 6 wherein the number of codes allocated to the firstnetwork user is limited by power and performance constraints.
 8. Aprocedure for admission control as set forth in claim 6 wherein thenumber of codes assigned to all network users is limited by power andperformance constraints.
 9. A procedure for admission control as setforth in claim 6 wherein successively smaller numbers of potential codesare tested for simultaneous activation until an acceptable overall powerallocation is found such that the code activation requests correspondingto the smaller numbers of potential codes is accepted.
 10. A procedurefor admission control as set forth in claim 6 wherein the acceptance ofthe number of codes terminates the admission process.
 11. A procedurefor admission control in a DS-CDMA network comprising: a) consideringnew potential codes for activation in increments of 1; b) checking eachnew code to make certain that there is a feasible power allocation forall active codes and each new potential code; and; c) admitting the newpotential code if the feasible power allocation exists; and rejectingthe potential code and terminating the procedure if the feasible powerdoes not exist.
 12. A procedure for admission control as set forth inclaim 11 wherein the feasible power allocation does not exist if thepower that would be required by all active users upon activation of thenew code, is greater than a maximum transmission power capability of allusers.
 13. A procedure for admission control as set forth in claim 12wherein the feasible power allocation further does not exist if areceived bit energy to noise power ratio minimum threshold target is notmet for the active codes.
 14. A method for implementing potential userson a DS-CDMA network comprising the following steps: a) relating datarates of all users in terms of powers; b) separating the users intodifferent power groups and selecting a power group for furtherprocessing; c) classifying the users into different data rate sets; d)deriving powers of the users in the different sets based on a maximumacceptable in-cell interference for the selected power group; e)determining data rates of the users from the derived powers; and f)selecting a different power group and undertaking the classifying,deriving and determining steps to provide various data rate and powerallocations.
 15. A method for implementing potential users as set forthin claim 14 further comprising the step of picking the allocation thatyields the highest sum of data rates for the users.
 16. A method forimplementing potential users as set forth in claim 14 wherein thedifferent power groups are arbitrarily separated, the separationcomprising maximum power limited and maximum power not limited.
 17. Amethod for implementing potential users as set forth in claim 14 whereinthe different rate sets comprises a first set of users at a minimum datarate, a second set of users at a maximum data rate, and a third set ofusers at a data rate between the minimum data rate and the maximum datarate.
 18. A method for implementing potential users as set forth inclaim 14 wherein the VG-CDMA network is one of local area network, widearea network, metropolitan area network and a fixed wireless network.19. A method for implementing potential users as set forth in claim 14wherein said separating step comprises the sub-step of considering thelocation of the users relative to a nearest reception/transmission cellof the network, placing the users operating at maximum power in view oftheir distance from the cell in a maximum power group.
 20. A method forselecting the optimum power and data rate to be used to maximize thethroughput through a DS-CDMA network comprising the following steps: a)organizing the users into the following sets: 0) users operating at lessthan the maximum power; 1) users not operating at the maximum data rateor the minimum data rate; 2) users operating at the minimum data rate;and 3) users operating at the maximum data rate; b) determining theconstant coefficients, which relate the powers of the users in sets 2and 3, to the powers of the users in set 1; c) determining the powers ofall users in set 1 in terms of the power of any single arbitrarilychosen user denoted by i. c) determining the power of the single userwith undetermined power s_(i) in set
 1. d) determining the power of theremaining users in set 1 and then determining the powers of the users insets 2 and 3; e) determining the total interferences generated by theusers in the network; f) determining the optimal power vector using themaximum value of interference; g) determining the optimal rateallocation for the particular choice of sets; and h) comparing the rateallocations for all possible combinations of the sets and solving for anoptimal rate allocation.
 21. A method for selecting the optimum powerand data rates as set forth in claim 20 wherein the total in-cellinterference in step e) is the sum of the received power of all users.22. A method for selecting the optimum power and data rate as set forthin claim 20 wherein the power of all users of the network are functionsof the total in-cell interference.
 23. A method for selecting theoptimum power and data rate as set forth in claim 20 wherein theorganizing of the users into the first set based on the power being usedis an in or out test based on the power levels of the users relative tothe maximum received power.
 24. A method for selecting the optimum powerand data rate as set forth in claim 23 wherein all users having powerlevels less than the maximum received power are included in the set. 25.A method for selecting the optimum power and data rates as set forth inclaim 20 wherein at the optimal power and rate allocation the rates ofthe interference experienced by any two users is equal to the squareroot of the reciprocal of their bit energy to noise targets.
 26. Amethod for selecting the power and data rates to be used tosubstantially maximize the throughput through a DS-CDMA networkcomprising the following steps: a) organizing users into the followingsets: 0) users having high values of signal to noise ratio; 1) userswith high signal to noise ratio requirements; 2) users with lower valuesof${{T^{m\quad m}\quad {where}\quad T} = \frac{\frac{E_{b}}{N_{o}}}{\frac{W}{r}}};$

3) users with lower values of T^(max) b) determining the constantcoefficients, which relate the powers of the users in sets 2 and 3 tothe powers of the users in set 1; c) determining the power of the usersin set 1 with the lowest maximum signal to noise ratio; d) determiningthe power of the remaining users in set 1 and then sets 2 and 3; e)determining the total interference of the users on the network; f)determining the power vector using the value of in-cell interference; g)determining the rate allocation based on the determined power vector; h)determining the power and data rate vector for all possibleclassifications of the users in the different sets. i) comparing therate allocations for all possible combinations of the above sets todetermine the optimal rate allocation the yields the maximum sum of thedata rates.
 27. A method for selecting the optimum power and data ratefor use in a DS-CDMA network comprising the following steps: a)organizing network users into sets based on their data rates; b)determining the constants that relate the powers of the latter setmembers to the power of the user in the earlier sets; c) determining thepower of the first member of the first set; d) determining the powers ofthe remaining members of the first set, and the power of all members ofthe remaining sets; e) determining the power vector from the totalin-cell interference; f) determining the rate allocation for theparticular choice of sets; and g) comparing the rate allocations asdetermined to select the optimal rate allocation.
 28. A method forselecting the optimum power and data rates as set forth in claim 27wherein the transmit powers have to be recalculated when a multi-mediauser changes data rates to meet a data transmission requirement.
 29. Amethod for selecting the optimum power and data rates as set forth inclaim 27 wherein the users are divided into sets based on the use ofmaximum rate, minimum rate, and a rate between maximum and minimum. 30.A method for selecting the optimum power and data rates as set forth inclaim 27 wherein at the optimal power and rate allocation, the ratio ofinterference experienced by the users is equal to the square root of thereciprocal of their bit energy to noise targets.
 31. A DS-CDMA networkcomprising: a plurality of users having different bit energy to noiserequirements; a limited number of potential codes available to be usedby the users; a limited overall power allocation available for each ofthe potential codes; and an admission protocol, the admission protocolmaximizing the capacity utilization within the network with the limitedoverall power budget.
 32. A DS-CDMA network as set forth in claim 31wherein the admission protocol arranges the networks in increasing orderbased on the bit energy to noise requirements.
 33. A DS-CDMA network asset forth in claim 32 wherein the admission protocol includes testing ofmultiple potential codes for generally simultaneous activation, thenumber of multiple potential codes being reduced until an acceptablethreshold is met.
 34. A DS-CDMA network as set forth in claim 33 whereinthe acceptable threshold is limited by the limited overall powerallocation such that code failure is minimized for every user within thenetwork.
 35. A DS-CDMA network as set forth in claim 31 wherein theadmission protocol includes: a second plurality of the users being atdifferent powers, the users being separated into different power groups;a third plurality of the users being at different data rates, the usersbeing separated into different data rate sets; and a maximum in-cellinterference being available for the users in each of the differentpower groups, wherein the allocation process optimizes the differentpowers and the different data rates to determine the data rate and thepower for each user.
 36. A DS-CDMA network as set forth in claim 35wherein the users are placed in at least two different power groups, afirst power group being limited in power and a second power groupoperational at maximum power.
 37. A DS-CDMA network as set forth inclaim 36 wherein a user at a high power in view of its remote locationfrom a nearest/transmission cell is placed into the second power group.38. A DS-CDMA network as set forth in claim 35 wherein the differentrate sets comprise a first rate set of users at a minimum data rate, asecond set of users at a maximum data rate, and a third set of users ata data rate between the minimum data rate and the maximum data rate.